1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device including an electrical fuse.
2. Description of the Related Art
Conventionally, there is known a technology in which a fuse is mounted on to a semiconductor device, whereby, for example, the electrical fuse is cut to adjust a value of a resistor used in the semiconductor device, or a defective element is separated and replaced by a normal element.
As a method of cutting a fuse, there is used a system of cutting the fuse by irradiating a part of the fuse with a laser beam, or a system of cutting the fuse through application of current.
JP 2005-39220 A, JP 2005-57186 A, and JP 2006-253237 A each disclose an electrical fuse which is cut with the use of a phenomenon in which a material forming the fuse migrates by electromigration.
JP 2005-39220 A discloses the fuse which is capable of being cut with a smaller current. In JP 2005-39220 A, an electrical conductor forming the fuse is formed in a shape in which the electrical conductor is folded back several times. Further, JP 2005-57186 A describes a structure in which lower and upper portions of a fuse melt down portion are covered with a plate, and side portions thereof are covered with via plugs.
JP 2006-253237 A describes a fuse element including a first interconnect, an insulating film formed above the first interconnect, a second interconnect formed above the insulating film, and a first via formed in the insulating film so as to connect the first interconnect and the second interconnect. In this case, a main portion of the first via is formed of a material which is more likely to cause the electromigration compared with main portions of the first interconnect and the second interconnect. JP 2006-253237 A also describes a structure in which heater wiring for heating the via is provided on the periphery of the via. Accordingly, it is intended that a temperature on the periphery of the via may be increased when the via is cut, whereby the via may be efficiently cut.
The present inventors have recognized as follows. As described in JP 2005-39220 A, JP 2005-57186 A, and JP 2006-253237 A, in a case where the fuse is cut with the use of the phenomenon in which the material forming the fuse migrates by the electromigration, for example, thermal treatment is performed on the semiconductor device after the fuse is cut, or the semiconductor device itself is exposed to heat generated in its actual use, whereby the material migrates. Accordingly, it is conceivable that reconnection may occur at a cutting point. If the reconnection as described above occurs, even when the electrical fuse to be cut is cut in advance, correct results cannot be obtained in a case of detecting whether or not the electrical fuse is cut. The fear that the reconnection as described above may occur is slight, and thus it is considered that no problem arises during normal operation. However, in a case where, for example, extremely high degree of reliability is required for the semiconductor device or the semiconductor device is used under extreme conditions, it is necessary to further enhance a retention characteristic that the cut electrical fuse maintains a state after cutting.
In order to solve the above-mentioned problems, in recent years, there is proposed a new method of cutting an electrical fuse, which is referred to as a crack assist type process, as described in JP 2007-305693 A (reference number: 74120620, Japanese Patent Application No. 2008-104277, and filing date: Apr. 14, 2008). In this method, for example, a structure of the electrical fuse and a voltage application method for the electrical fuse are controlled, whereby a part of the electrical conductor that forms the electrical fuse is forced to flow outside the electrical fuse, that is, flow into an insulating film provided on the periphery of the electrical conductor when the electrical fuse is cut. Then, a balance between a migration and a supply of a material is disturbed, to thereby form a cutting point with larger void in other part. As a result, a fear that the cut electrical fuse may be reconnected may be significantly reduced, and hence an excellent state after cutting may be maintained.
However, a flowing amount of the electrical conductor is increased in the electrical fuse cut by the above-mentioned method, and hence it is necessary to control a flowing portion of the electrical conductor and the migration of the flowing electrical conductor.